The present invention is directed to a tubular manifold for a heat exchanger, and more particularly, to a manifold that is D-shaped in cross-section and formed by extrusion.
Currently, single piece manifolds are made from roll-formed, welded tubing, and are available in gauges from 0.040 inch (0.1016 cm) to 0.065 inch (0.1651 cm) and diameters up to 1.50 inch (3.81 cm). Although parallel flow technology has been widely adopted in the automotive industry, it has not been adopted in the HVAC industry. From a manifold standpoint, two basic problems have arisen in applying parallel flow technology to the HVAC industry. First, the price per pound for the manifolds is too high (averaging about $11.00 per pound in 2000) and second, the burst pressure is too low for the newer refrigerants (pressures in the HVAC industry being much higher than in the automotive industry).
In addition, the current method of manufacturing manifolds, using piercing dies, makes it difficult to create samples for customers. The tooling for a manifold is designed around the individual customer""s centerline spacing, which involves both the tube and fin height and width. The tooling is very expensive and usually requires long lead times for design, development, and fabrication. Currently, tooling only exists for a limited number of sizes and centerlines, and these available sizes and centerlines may not meet a particular customer""s needs. An increase in the existing gauge of the tubing also requires a significant tooling charge for forming rolls on tube mills. Tubing suppliers generally are not willing to bear this expense unless the customer can guarantee a large order or pay the up-front tooling cost.
Despite these disadvantages, roll-formed, welded tubing has several advantages. Once the correct gauge is selected, the tube mills can produce the tubing at a high rate of speed, the product is very consistent, and braze cladding is already a constituent of the material being welded.
Thus, there is a need for a tubular manifold that has a higher burst pressure and is less expensive than roll-formed, welded manifolds, but that can be manufactured quickly, and with the consistency of roll-formed, welded manifolds.
It is to the solution of these and other problems that the present invention is directed.
It is therefore an object of the present invention to provide a tubular manifold that has a burst pressure high enough for the newer refrigerants.
It is another object of the present invention to provide a tubular manifold that is economical to manufacture.
It is still another object of the present invention to provide a tubular manifold in which the size, centerline, and gauge can all easily and inexpensively be customized.
It is still another object of the present invention to provide a tubular manifold that can be manufactured at a high rate of speed while maintaining consistency of the product.
These and other objects of the present invention are achieved by the provision of a one-piece, seamless, D-shaped manifold that is machined from extruded tubing rather than from roll-formed, welded tubing. The extruded tubing has a substantially flat part and a concavely curved part, so as to be substantially D-shaped in cross-section. The substantially flat part, which forms the manifold header, is thicker than the concavely curved part, which forms the manifold tank, in order to provide improved burst strength. At least two longitudinal ribs (hereafter referred to as external ribs) are formed on the header exterior, preferably positioned symmetrically relative to the longitudinal center line of the header. The external ribs provide additional strengthening of the header and act as stops to prevent the heat exchanger fins from contacting the tube/manifold joint and the substantially flat outer surface of the header (which can lead to leakage when the joint is brazed). The number of external ribs and their location will depend on the size of the manifold and the precision required in positioning the heat exchanger tubes in the slots.
Slots for insertion of heat exchanger tubes through the header are formed by machining, during which the adjoining edges of the external ribs are chamfered. Alternatively, the slots are roughed out by sawing, then finalized by milling, and during milling, the adjoining edges of the external ribs are chamfered. The chamfering of the external rib edges has the added advantage of providing a guide surface for the heat exchanger tubes as they are inserted into the tube slots.
Cladding is applied on the outside of the finished manifold. The substantially flat exterior surface of the header provides a better surface for applying the cladding than a tube having a totally circular cross-section. During brazing, the cladding melts to seal the tube/manifold joints.
The manifold can be extruded with lengthwise ribs (hereafter referred to as internal ribs) extending along the interior sides of the tank to act as stops for the heat exchanger tubes.
Baffles can be placed between selected tube slots by machining a cut into the same surface as the tube slots, that is, into the header. The cut can extend into the tank. The baffles are driven into place with a press. Baffles can also be placed in cuts adjacent the ends of the manifold to serve as end caps.